The invention relates to a method for assessment of the phase angle of a camshaft of an internal combustion engine, in particular for a motor vehicle.
In internal combustion engines which are used in motor vehicles, the mixture is supplied to the individual cylinders of the internal combustion engine via inlet valves which are operated by the camshaft. Internal combustion engines exist, in which the inlet control times can be set such that they are variable. This is achieved by using variable phase camshafts. With these camshafts, the camshaft is displaced relative to the driving pinion. If the present setting is detected by means of a camshaft sensor fitted on the drive pinion, this does not allow the phase adjustment to be monitored at the same time, so that the phase adjustment thus cannot be determined reliably.
The invention is thus based on the object of specifying a method for checking the phase adjustment of a camshaft, during which check the present phase angle of a variable phase camshaft can be detected reliably.
According to the invention, the object is achieved in that a first value which corresponds to the actual noise level of the internal combustion engine is determined during a predetermined evaluation window, is compared with a second value which corresponds to the actual noise level after phase adjustment of the camshaft, and the operation of the phase adjustment of the camshaft is assessed as a function of this comparison.
The advantage of the invention is that the phase angle and adjustment of the camshaft are detected solely by an indirect measurement of the noise level of the internal combustion engine. This makes use of the fact that the inlet valves arranged on the individual cylinders of the internal combustion engine produce closing noises which can be measured well. These noise peaks are detected and are used to determine the camshaft phase angle.
The correct operation of the phase adjustment of a variable phase camshaft is determined reliably in that the first value, which corresponds to the actual noise level, is determined during the first evaluation window for a first setting of the variable phase camshaft, and a second value, which corresponds to the actual noise level, is then determined for a second setting of the variable phase camshaft, with the noise level values determined for the two settings being formed into a ratio of one to the other in order to assess the phase adjustment of the camshaft.
The ratio formation eliminates the basic noise of the internal combustion engine.
The position and length of the evaluation window are chosen such that at least one closing noise of the inlet valves operated by the camshaft is detected at the first setting of the camshaft within the evaluation window, and the closing noise of the inlet valves can no longer be detected in the evaluation window at the second setting of the camshaft.
In a development of the invention, a third value of the noise level for the first selected setting of the camshaft and a fourth value of the noise level for the second selected setting of the camshaft are determined during a second predetermined evaluation window which preferably follows the first predetermined evaluation window in time, with the third and the fourth noise level values being formed into a ratio of one to the other.
The use of a second evaluation window improves the reliability of diagnosis of the phase adjustment of the camshaft. In addition, in the event of a fault (no phase adjustment), the actual phase angle of the camshaft is identified using the second evaluation window.
Advantageously, the ratio of the first value to the second value of the noise level and/or the ratio of the third value and the fourth value of the noise level are each compared with a reference value, and, if the reference value is exceeded, correct twisting of the camshaft is identified.
In a development, the first and/or the second evaluation window are/is set as a function of the angle position of a crankshaft, by which means the measurement window can be reproduced at any time.
In a refinement, a number of values which are measured for one setting of the camshaft and correspond to the actual noise load are averaged, and this mean value is used as the basis for assessing the phase adjustment of the camshaft.
A structure-borne sound sensor, which is arranged on the internal combustion engine for antiknock control, is used to assess the camshaft adjustment, with the predetermined evaluation windows for determining the camshaft adjustment being opened only when other measurement operations, which are dependent on the signal from the structure-borne sound sensor, are inactive. In this way, the time period for determining the camshaft position differs, for example, from the time period of ignition adjustment.
The invention allows numerous embodiments. One of these will be explained in more detail with reference to the figures which are illustrated in the drawing, in which: